RULE II.—OTHER FINALS.
Words ending in any other consonant than f, l, or s, do not double the final letter; as, mob, nod, dog, sum, sun, cup, cur, cut, fix, whiz.
EXCEPTIONS.—We double the consonant in abb, ebb, add, odd, egg, jagg, ragg, inn, err, burr, purr, butt, buzz, fuzz, yarr, and some proper names. But we have also ab (from) and ad (to) for prefixes; and jag, rag, in, bur, and but, are other words that conform to the rule.